JP2002314465A - Hands-free phone - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that a conventional hands-free phone having a hybrid transformer for 2/4-wire conversion placed in a communication line between a speaker and a microphone an amplifier connected respectively to them, causes howling when the microphone amplifier is set to a high fixed gain or obtains only a small sound volume heard from a receiver of the phone when the microphone amplifier is set to a low fixed gain. SOLUTION: The hands-free phone is characterized in that attenuators controlling a transmission signal and a reception signal are placed in the communication line, a level detector is provided before and after the attenuators to compare the transmission signal and the reception signal and an attenuator control is placed to conduct half duplex control on the basis of signals from both the level detectors.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a half-duplex hands-free phone.

[0002]

2. Description of the Related Art A conventional hands-free phone uses an AGC circuit (auto gain control) for a signal input from a microphone and keeps the output signal level constant regardless of the level of the microphone input signal. That is,
When the distance between the microphone and the mouth is large and the microphone input signal is small, the gain of the microphone amplifier is increased. Conversely, when the distance between the microphone and the mouth is short and the microphone input signal is large, the gain of the microphone amplifier is reduced.

Alternatively, as shown in FIG. 7, an output signal is made proportional to an input signal. That is, the microphone amplifier 55
Gain G = 20 × log (51 kΩ / 5.1 kΩ) =
It was kept constant at 20 dB. As shown in FIG. 8, a conventional hands-free phone generally uses full-duplex communication for simultaneous transmission and reception.

In full-duplex communication, amplifiers 55, 5
Sound from a speaker 50 having a microphone 6
There is an acoustic coupling that causes sound to be collected, and a line coupling where the signal transmitted to the circuit side is reflected by the hybrid transformer 52 and received again. Both of these cause howling. Echo cancellers 53 and 54 are used to prevent howling due to acoustic coupling and circuit coupling.
These two echo cancellers have the function of comparing the transmitted signal and the received signal and canceling them.

[0005]

According to such a hands-free phone, when a microphone amplifier having a fixed gain is used, howling is caused when the gain is increased, and the mouth is separated from the microphone when the gain is reduced. In such a case, there is a problem that the volume heard from the receiver of the other party's telephone is reduced.

Further, the echo canceller has a limit in the signal level that can be canceled. If the output signal level of the speaker is increased or the gain of the microphone amplifier is increased to increase the input signal level, the echo canceller becomes a limit and howling occurs. There is a problem that occurs. Further, the echo canceller has a problem that a transmission signal is reduced because a signal collected from a microphone is also attenuated.

[0007]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a hands-free phone having a hybrid transformer for performing two-wire to four-wire mutual conversion in a communication path between a speaker and a microphone each having an amplifier connected thereto. , An attenuator for controlling the transmission signal and an attenuator for controlling the reception signal, a level detector for comparing the transmission signal and the reception signal before and after both attenuators, and a half-duplex signal from the two level detectors. An attenuator control for performing control is provided. Furthermore, the microphone amplifier is provided with a slice circuit using a diode.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram of a half-duplex system, and FIG. 2 is a circuit diagram of a microphone amplifier, in which two diodes 4 and 5 are connected. FIG. 3 shows a signal waveform by the microphone amplifier of FIG.
Is the input signal waveform to the microphone amplifier, (2) is the output signal 6 waveform when the signal input to the microphone amplifier is small,
(3) is the waveform of the output signal 7 when the signal input to the microphone amplifier is large.

FIG. 4 is an explanatory diagram of a connection state of the hands-free phone. In the figure, a hands-free phone 13 installed in a private house 11 is connected to a public network 15 and a telephone set 14 similarly installed in a private house 12 is shown. It is connected to the public network 15. FIG. 5 is an explanatory diagram of a front panel of the handsfree phone. In the figure, 21 is a push button,
Reference numeral 22 denotes a speaker that outputs the voice of the other party and a synthesized voice from the public network 15, and 23 denotes a speakerphone button used when using the hands-free phone function.
Reference numeral 4 denotes a microphone that collects the voice of the hands-free phone user.

In FIG. 1, reference numeral 22 denotes a speaker for sounding a signal received from the public network 15 as described above, reference numeral 24 denotes a microphone for collecting the voice of a hands-free phone user as described above, and reference numeral 32 denotes a microphone input signal. Amplifying microphone amplifier, 33, a transmitting amplifier for amplifying a signal to be transmitted to the public network 15, 34, a hybrid transformer for performing two-wire to four-wire mutual conversion of a communication path, and 35, a receiving amplifier for amplifying a received signal from the public network 15. An amplifier 36 is a speaker amplifier for amplifying power for driving the speaker 22.

Reference numeral 38 denotes a transmission signal TLIA, 39 denotes a reception signal RLIA, 40 denotes a transmission signal TLIB, and 41 denotes a reception signal RLI.
LIB. 42 is a level detector A, and the TL
Compare IA38 and RLIA39. Reference numeral 43 denotes a level detector B, which compares the TLIB 40 with the RLIB 41. Attenuator control 44 performs half-duplex control based on signals from the level detector A42 and the level detector B43.

Reference numeral 45 denotes a TX attenuator for controlling a transmission signal, and reference numeral 46 denotes an RX attenuator for controlling a reception signal. The half-duplex control operation by the above circuit will be described with reference to the flowchart of FIG. A case where a call is made from the hands-free phone 13 of the private house 11 to the telephone 14 of the private house 12 using the public network 15 will be described.

First, when the speakerphone button 23 is pressed, a tone signal sounds from the speaker 22. The telephone number of the private house 12 is pressed by the push button 21. A ring back tone (hereinafter referred to as RBT) that is ON for 1 second and OFF for 2 seconds sounds from the speaker 22 of the private house 12.
At this time, the telephone 14 of the private house 12 is also ON for 1 second and OF for 2 seconds.
A ringing tone sounds at F.

When the receiver of the telephone 14 of the private house 12 is off-hook, the ringing tone stops, and a telephone call can be made between the hands-free telephone 13 of the private house 11 and the telephone 14 of the private house 12. The voice of the conversation is collected by the microphone 24 and amplified by the microphone amplifier 32. The transmission signal TLIA 38 amplified by the microphone amplifier 32 is input to the level detector A 42 and the TX attenuator 45.

The level detector A42 receives the received signal R
LIA 39 is also input. The half-duplex system operates as follows. At the time of transmission, the level detector A42 transmits the transmission signal T
Compare the level of the LIA 38 and the level of the received signal RLIA 39,
When TLIA> RLIA, the level detector A 42 detects transmission and transmits a switching message to the attenuator control 44. Upon receiving this switching message, the attenuator control 44 turns off the TX attenuator 45,
X Turn on the attenuator 46.

At the time of reception, the level detector B43 compares the level of the transmission signal TLIB40 with the level of the reception signal RLIB41. If TLIB <RLIB, the level detector B43 is used.
And detects the reception, and transmits a switching message to the attenuator control 44. Upon receiving this switching message, the attenuator control 44 turns on the TX attenuator 45,
The RX attenuator 46 is turned off.

The transmission signal TLIA3 is detected by the level detector A42.
8 is compared with the level of the received signal RLIA 39. If the state of TLIA> RLIA continues for about 1 second, the level detector A 42 detects the received signal and transmits a switching message to the attenuator control 44. Upon receiving this switching message, the attenuator control 44 turns off the TX attenuator 45 and turns on the RX attenuator 46.

At the time of transmission, the voltage is amplified by the transmission amplifier 33 and output to the telephone line. The signal is converted from four wires to two wires by the hybrid transformer 34, but at this time, all signals do not propagate to the telephone line but go around to the receiving amplifier 35 side. The sneak signal is amplified by the receiving amplifier 35, but since the RX attenuator 46 is ON, howling due to line coupling does not occur. Further, since the transmitting side and the receiving side operate alternately, even if the sound that is sounded by the speaker 22 during reception is collected by the microphone 24, the howling due to acoustic coupling does not occur because the TX attenuator 45 is ON.

When the call is over, hands-free phone 1
3 is pressed to close the line. The receiver of the telephone 14 is hooked on. According to the present embodiment described above, it is possible to prevent the occurrence of howling due to acoustic coupling and line coupling, thereby increasing the speaker level of a hands-free phone.

Second Embodiment In order to construct a high-quality hands-free phone for reporting an emergency, sufficient conversation must be made even at a distance from the hands-free phone. At the time of transmission, the level of the transmission signal TLIA 38 and the level of the reception signal RLIA 39 are compared by the level detector A42. In the case of the conventional microphone amplifier shown in FIG. 1, the signal output to the telephone line becomes extremely small, and the volume heard from the handset of the telephone 14 of the private house 12 is low, and there is a problem that it is difficult to hear.

The level detector A42 transmits the transmission signal TL
The level of the IA 38 and the level of the received signal RLIA 39 are compared. When the gain of the microphone amplifier 32 is adjusted to a position close to the mouth of the microphone, in the case of the conventional microphone amplifier as shown in FIG. Transmission signal T
The level of the LIB 40 and the level of the received signal RLIB41 are compared. However, since the amplification factor of the microphone amplifier 32 is extremely high, there is a problem that TLIB <RLIB is not satisfied, and the receiving state cannot be switched.

In this embodiment, the problem is solved by using a microphone amplifier as shown in FIG. The microphone amplifier shown in FIG. 2 has a gain G
= 20 × log (180 kΩ / 5.1 kΩ) = about 31 d
B.

Consider a case where the diodes 4 and 5 are present. The forward voltage of the diodes 4 and 5 is VF. VF is usually 1V. If the output signal of the microphone amplifier is a positive voltage and becomes equal to or higher than VF of the diode 4, the negative input 3 of the operational amplifier is logically short-circuited to 0V, so that it is clipped at + 1V. The clipped state is shown in FIG.

When the output signal of the microphone amplifier becomes a negative voltage and becomes equal to or lower than VF of the diode 5, the operational amplifier negative input 3
Is logically short-circuited to 0V, so it is clipped at -1V. The clipped state is shown in FIG. Since the bare gain of the microphone amplifier shown in FIG. 1 is about 31 dB, the input signal 1 that the amplifier does not clip at +1 V or -1 V is about ± 28 mV. Therefore, FIG.
(1) the amplitude C of the input signal when the following 56m V _pp, sine wave as shown in FIG. 3 (2) output signal 6 is outputted from an output signal 2. On the other hand, the amplitude C of the input signal shown in FIG.
When the voltage is _{equal to} or higher than V _pp , as shown in FIG.
The signal clipped with V is output from the output signal 2.

Hereinafter, the microphone and the talker's mouth are close to each other during a call.
A comparison will be made between a time and a distance. When the microphone is close to the mouth When the microphone is close to the mouth, the input signal of the microphone amplifier 32 is
Signal amplitude is about 56mV _ppThat is all.

Therefore, the output voltage of the microphone amplifier 32 is clipped at about 2 V _pp , and becomes the output signal 7 in FIG. Thereby, at the time of reception, the level detector B43
, The level of the transmission signal TLIB40 and the level of the reception signal RLIB41 are compared. When the output voltage becomes 2 V _pp or more, the output voltage of the microphone amplifier 32 is limited to 2 V _pp or less with respect to the reception signal RLIB41. Problem can be solved.

When the mouth is far from the microphone The voice spoken is collected by the microphone 31 and amplified by the microphone amplifier 32. If the microphone is too far from the mouth, use the microphone amplifier 32
Becomes less than about 56 mV _pp . Therefore, the output voltage of the microphone amplifier 32 is about 2 V _pp or less, and the output signal is as shown in FIG. As a result, the signal output to the telephone line can be increased, and the problem that it is difficult for the telephone 14 of the private house B to hear the signal can be solved.

FIG. 3C shows a clipped waveform like the output signal 7, but since the frequency band includes the voice band, the voice maintains a quality that does not cause a problem in conversation. When the call is over, the speakerphone button 23 of the hands-free phone 13 is pressed to close the line. The receiver of the telephone 14 is hooked on. According to the present embodiment described above, by providing a slice circuit using a diode in the microphone amplifier, a large volume level can be output to the telephone line even when the mouth is far from the microphone. Further, the half-duplex system can suppress howling due to acoustic coupling even when the microphone is close to the mouth. Furthermore, the switching failure of the half-duplex system is improved.

Third Embodiment In a call state, transmission, that is, transmission from the hands-free phone 13 of the private house A 11 to the telephone 14 of the private house B 12 has priority. That is, the transmission signal TLIA is detected by the level detector A42.
38 is compared with the level of the received signal RLIA39. In the initial state, RLIA3 is set so that TLIA> RLIA.
The signal level of the TLIA 38 is set a little higher than 9, and the transmission is detected by the level detector A42, and the switching message is transmitted to the attenuator control 44. Upon receiving the switching message, the attenuator control 44 turns off the TX attenuator 45 and turns on the RX attenuator 46.

At the time of reception, the level detector B43 compares the level of the transmission signal TLIB40 with the level of the reception signal RLIB41. If TLIB <RLIB, the level detector B43 detects reception and transmits a switching message to the attenuator control 44. I do. Upon receiving the switching message, the attenuator control 44 turns on the TX attenuator 45 and turns off the RX attenuator 46.

When the call is over, hands-free phone 1
3 is pressed to close the line. The receiver of the telephone 14 is hooked on. According to the above-described embodiment, by giving priority to the call from the hands-free phone, when using the hands-free phone in an emergency or the like, the caller does not need to do anything other than report the message. Can be sent to the recipient.

[0032]

According to the present invention described in detail above, it is possible to prevent the occurrence of howling due to acoustic coupling and line coupling, thereby increasing the speaker level of a hands-free phone. Further, by providing a slice circuit using a diode in the microphone amplifier, there is an effect that a large volume level can be output to the telephone line even when the mouth is far from the microphone. Further, the half-duplex method has an effect that howling due to acoustic coupling can be suppressed even when the microphone is close to the mouth. There is an effect that the switching failure of the half-duplex system is improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a half-duplex system

FIG. 2 is a circuit diagram of a microphone amplifier.

FIG. 3 is a signal waveform obtained by the microphone amplifier of FIG. 2;

FIG. 4 is an explanatory diagram of a connection state of a hands-free phone;

FIG. 5 is an explanatory view of a front panel of the handsfree phone.

FIG. 6 is a flowchart of a half-duplex control operation.

FIG. 7 is a circuit diagram of a conventional microphone amplifier.

FIG. 8 is a circuit diagram of a full-duplex system.

[Explanation of symbols]

 Reference Signs List 1 input signal 2 output signal 3 operational amplifier negative input 4 diode 5 diode 6 output signal 7 output signal 11 private house 12 private house 13 hands-free phone 14 telephone 15 public network 21 push button 22 speaker 23 speakerphone button 24 microphone 32 microphone amplifier 33 transmission amplifier 34 hybrid transformer 35 reception amplifier 36 speaker amplifier 38 transmission signal TLIA 39 reception signal RLIA 40 transmission signal TLIB 41 reception signal RLIB 42 level detector A 43 level detector B 44 attenuator control 45 TX attenuator 46 RX attenuator

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5D020 CC00 5K027 BB03 DD02 DD08 HH03 5K046 AA01 BB01 CC29 DD01 DD11 DD18

Claims (3)

[Claims] 1. A hands-free phone having a hybrid transformer for performing two-wire to four-wire mutual conversion in a communication path between a speaker and a microphone each connected to an amplifier. Providing an attenuator for controlling the signal, providing a level detector for comparing the transmission signal and the reception signal before and after both attenuators, and providing an attenuator control for performing half-duplex control based on the signals from the two level detectors A hands-free phone characterized by the following. 2. The hands-free phone according to claim 1, wherein a slice circuit using a diode is provided in the microphone amplifier. 3. A hands-free method according to claim 1, wherein in an initial state, a signal level is set so that a transmission signal is greater than a reception signal, a level detector detects transmission, and switches to attenuator control to transmit a message. A hands-free phone that gives priority to calls from the phone.